1. Field of the Invention
The present invention relates to plant growth regulators, and more particularly, to the enhancement of production of polyisoprene rubber.
2. Description of the Prior Art
Guayule is a desert shrub native to the southwestern United States and northern Mexico that produces polymeric isoprene essentially identical to that made by Hevea rubber trees in Southeast Asia. As recently as 1910 it was the source of half of the natural rubber used in the U.S. Since 1946, however, its use as a source of rubber has been all but abandoned in favor of cheaper Hevea rubber and synthetic rubbers. However, demand for natural rubber is expected to produce shortages of that material as early as 1980 and rubber prices are expected to double by 1985. Natural rubber having lower heat hysteresis is required for many kinds of tires and amounts to about 35% of U.S. rubber use.
It is technically possible to satisfy projected demand with synthetics, but the rise in world petroleum prices has prompted the rubber industry to look for alternative sources of natural rubber. The principal, if not the only such, source is Guayule. It is conceivable that Guayule eventually could replace Hevea trees because of the susceptibility of the Hevea tree to a number of devastating diseases.
To minimize dependence on dwindling supplies of fossil fuel, attention is being directed to the production of hydrocarbons in plants such as Hevea and Guayule.
Guayule plants thrive on the dry, sandy soil of southwestern U.S. and Mexico. During World War II, extensive plantings of Guayule were carried out in California, near Indio and Salinas. Guayule normally yields one half ton of rubber per acre in cultivation when, after two years, the entire plant is harvested and processed. Various known Hevea tree latex modifiers, such as Etherill (2-ethyl phosphonic acid), which boost latex yield in Hevea trees by preventing clotting of flowing latex will not work with Guayule plants. In Guayule the latex is present as tiny inclusions in the bark, which are not interconnected. The literature suggests that no known plant regulator mechanism was applicable to Guayule, or that if any growth enhancement ever were to be achieved, it would have to come by way of a biochemical modification of the membrane process which produces the polyisoprenic latex.